Tube couplings comprising a socket and plug have been made of metal or plastics depending upon the application intended. However, there is still much to be desired with respect to anti-corrosion properties, temperature resistance and sealing properties.
Valve means for opening and closing flow passage means through the socket and/or plug is usually arranged to be biased toward its closed position by a compression coil spring made of metal and to be retracted to its open position against the biasing force of the coil spring when the tube coupling is connected. However, being made of metal, conventional compression coil springs had the disadvantage that they are susceptible to rust and corrosion as they are exposed to fluid. There is thus a room for improvement on resistance to chemicals and corrosion.
Seal rings are usually mounted in the interior of the socket and/or plug to prevent fluid leakage due to lack of sealing integrity. However, such seal rings usually formed of rubber have weak points with respect to resistance to chemicals, corrosion and temperature. There have been no tube coupling that is suitable for use to handle fluids containing corrosive chemicals such as strong acids.